<title>Characteristics of ice-active substances released by sea-ice diatoms</title>

Abstract

Several species of antarctic sea ice diatoms have been found to release ice-active substances (IAS). At natural concentrations, they produce dense pitting on ice crystal surfaces at temperatures slightly below the freezing point, without significantly affecting the freezing point. This phenomenon appears to be associated with cold-adapted species as it has not been found in temperature fresh water and marine diatoms. IASs have been found in several species of sea ice diatoms, including both attached and unattached species. The ice-active substances have been found both in ice platelet water as well as in the solid congelation ice in McMurdo Sound in early summer, and in newly formed ice in winter in the Weddell and Bellinghausen seas. An IAS- producing species (Amphiprora) was cultured in the laboratory and produced noticeable increases in IAS activity. The IAS is retained by dialysis tubing and appears to be proteinaceous, as it is inactivated by proteases and heat. Further attempts to purify and characterize the IAS are in progress. The role of the IAS is unknown. Possible roles involving attachment of diatoms to ice and modification of the optical properties of ice are being considered.